Method for removal of residue from a substrate

ABSTRACT

A method for removing residues from a substrate. The residue is removed by exposing the substrate to a hydrogen-based plasma. After the substrate is exposed to the hydrogen-based plasma, the substrate may optionally be immersed in an aqueous solution including hydrogen fluoride.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a method offabricating devices on semiconductor substrates. More specifically, theinvention relates to a method for removal of residue from asemiconductor substrate.

[0003] 2. Description of the Related Art

[0004] Microelectronic devices are generally fabricated on asemiconductor substrate as integrated circuits wherein various metallayers are interconnected to one another to facilitate propagation ofelectrical signals within the device. One typical process used forfabrication of the microelectronic devices is a plasma etch process.During plasma etch processes, one or more layers that comprise a metal(e.g., tantalum (Ta), titanium (Ti), and the like) or a metal-basedcompound (e.g., tantalum nitride (TaN), titanium nitride (TiN), and thelike) are removed, either partially or in total, to form a feature(e.g., interconnect line or contact via) of the integrated circuit.

[0005] Generally, plasma etch processes use gas chemistries that, whenreacted with the material comprising the etched layer or etch mask, mayproduce non-volatile by-products. Such by-products accumulate on thesubstrate as a residue. In the art, such residue is commonly called a“post-etch residue.” Post-etch residues interfere with processing of thesubstrate, e.g., the residues may contaminate the remaining layers orcause difficulties in depositing subsequent layers. Metal-containingresidue may also cause short-circuits that disrupt or degrade operationof the integrated circuits.

[0006] Conventional methods for removing residues typically includemultiple wet treatments of the substrate with an intermediate plasmastrip process using an oxygen-based chemistry. Multiple wet treatments,along with an intermediate plasma strip process (i.e., etch and stripprocesses), reduce productivity during fabrication of themicroelectronic devices. Further, the oxygen-based plasma strip processmay form hard to remove metal oxides on the substrate.

[0007] Therefore, there is a need in the art for an improved method forremoving residue from a substrate during fabrication of microelectronicdevices.

SUMMARY OF THE INVENTION

[0008] The present invention is a method for removing residue from asubstrate. The residue is removed by exposing the substrate to ahydrogen-based plasma. After the substrate is exposed to thehydrogen-based plasma, the substrate may optionally be immersed in anaqueous solution including hydrogen fluoride. In one application, theresidue comprises at least one metal (e.g., tantalum (Ta), titanium(Ti), tungsten (W), hafnium (Hf), and the like).

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The teachings of the present invention can be readily understoodby considering the following detailed description in conjunction withthe accompanying drawings, in which:

[0010]FIG. 1 depicts a flow diagram of a method for removing residue inaccordance with an embodiment of the present invention;

[0011]FIGS. 2A-2D depict a sequence of schematic, cross-sectional viewsof a substrate having a film stack where residue is removed inaccordance with the method of FIG. 1;

[0012]FIG. 3 depicts a schematic diagram of an exemplary plasmaprocessing apparatus of the kind used in performing portions of theinventive method; and

[0013]FIG. 4 is a table summarizing the processing parameters of oneexemplary embodiment of the inventive method when practiced using theapparatus of FIG. 3.

[0014] To facilitate understanding, identical reference numerals havebeen used, where possible, to designate identical elements that arecommon to the figures.

[0015] It is to be noted, however, that the appended drawings illustrateonly exemplary embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

DETAILED DESCRIPTION

[0016] The present invention is a method for removing residue from asubstrate (e.g., silicon (Si) wafer, gallium arsenide (GaAs) wafer, andthe like) during fabrication of a microelectronic device. In oneapplication, the inventive method is used to remove post-etch residuethat comprises at least one metal (e.g., tantalum (Ta), titanium (Ti),tungsten (W), hafnium (Hf), and the like), as well as compounds thereof.

[0017]FIG. 1 depicts a flow diagram of one embodiment of the inventivemethod for removal of residue as sequence 100. The sequence 100 includesprocesses performed upon a film stack having at least one metal layer.

[0018]FIGS. 2A-2D depict a series of schematic, cross-sectional views ofa substrate having a film stack from which residue is removed usingsequence 100. The cross-sectional views in FIGS. 2A-2D relate toindividual processing steps performed upon the film stack. The images inFIGS. 2A-2D are not depicted to scale and are simplified forillustrative purposes.

[0019] The sequence 100 starts at step 101 and proceeds to step 102 whena film stack 202 and etch mask 204 are formed on a wafer 200, e.g.,silicon wafer (FIG. 2A). In one embodiment, the film stack 202 comprisesa barrier layer 210, a metal-containing layer 208, and an insulatinglayer 206.

[0020] The barrier layer 210 and insulating layer 206 are generallyformed of a dielectric material, such as silicon nitride (Si₃N₄),silicon dioxide (SiO₂), hafnium dioxide (HfO₂), and the like, to athickness of about 300 to 600 Angstroms. The metal-containing layer 208is formed from tantalum nitride (TaN), tantalum (Ta), titanium (Ti),tungsten (W), and the like or compounds thereof, to a thickness of about600 to 1000 Angstroms.

[0021] The layers of the film stack 202 can be formed using anyconventional thin film deposition technique, such as atomic layerdeposition (ALD), chemical vapor deposition (CVD), plasma enhanced CVD(PECVD), physical vapor deposition (PVD), and the like. Fabrication ofthe microelectric devices may be performed using the respectiveprocessing reactors of CENTURA®, ENDURA®, and other semiconductor waferprocessing systems available from Applied Materials, Inc. of SantaClara, Calif.

[0022] The etch mask 204 is formed on the insulating layer 206 (FIG.2A). The etch mask 204 protects a region 220 of the film stack 202 whileexposing adjacent regions 222 of the stack 202. Generally, the etch mask204 is a photoresist mask that is fabricated using a conventionallithographic patterning process. For such process, a photoresist layeris exposed through a patterned mask, developed, and the undevelopedportion of the photoresist is removed. The photoresist mask 204typically has a thickness of about 2000 to 6000 Angstroms.

[0023] Alternatively, the etch mask 203 may be a hard mask formed ofsilicon dioxide (SiO₂), Advanced Patterning Film™ (APF) (available fromApplied Materials, Inc. of Santa Clara, Calif.) and hafnium dioxide(HfO₂).

[0024] The etch mask 204 may further comprise an optionalanti-reflective layer 205 (shown in broken line) that controls thereflection of the light during exposure of the photoresist. As featuresizes are reduced, inaccuracies in an etch mask pattern transfer processcan arise from optical limitations that are inherent to the lithographicprocess, such as the light reflection. The anti-reflective layer 205 maycomprise, for example, silicon oxi-nitride, polyamides, and the like.

[0025] Processes of applying the etch mask 204 are described, forexample, in commonly assigned U.S. patent application Ser. No.10/245,130, filed Sep. 16, 2002 (Attorney docket number 7524) and Ser.No. 09/590,322, filed Jun. 8, 2000 (Attorney docket number 4227), whichare incorporated herein by reference.

[0026] At step 104, the insulating layer 206 and the metal-containinglayer 208 are plasma etched and removed in the unprotected regions 222(FIG. 2B). The insulating layer 206 and the metal-containing layer 208may be etched using either a chlorine-based gas mixture or,alternatively, a fluorine-based gas mixture. The chlorine-based gasmixture may comprise chlorine (Cl₂), BCL₃ and an inert diluent gas, suchas at least one of argon (Ar), helium (He), neon (Ne), and the like,along with a small amount of a carbon-containing gas, such as carbontetrafluoride (CF₄) and the like. Alternatively, the fluorine-based gasmixture may comprise carbon tetrafluoride (CF₄), CHF₃ or SF₆ and aninert diluent gas, such as at least one of argon (Ar), helium (He), neon(Ne), and the like.

[0027] In one embodiment, step 104 uses the mask 204 as an etch mask andthe barrier layer 210 as an etch stop layer. Specifically, duringetching of the metal-containing film 208, the endpoint detection systemof the etch reactor may monitor plasma emissions at a particularwavelength to determine an end of the etch process. Conventionally, theetch process continues until a shallow recess 224 is formed in thebarrier layer 210 (FIG. 2B). The shallow recess 224 is formed to a depth226 of not greater than about 150 Angstroms, e.g., typically about 50 to75 Angstroms. Such recess 224 facilitates removal of themetal-containing layer 208 (e.g., tantalum nitride (TaN)) from thebarrier layer 210 in the regions 222.

[0028] Step 104 can be performed in an etch reactor such as a DecoupledPlasma Source (DPS) reactor of the CENTURA® system, commerciallyavailable from Applied Materials, Inc. of Santa Clara, Calif. The DPSreactor uses a source of radio-frequency (RF) power at about 50 kHz to13.56 MHz to produce a high-density inductively coupled plasma.

[0029] During step 104, a portion of the material removed from theinsulating film 206 and the metal-containing layer 208 combine withcomponents of the etchant gas mixture (e.g., chlorine-containing orfluorine-containing gases and the like), as well as with the componentsof the etch mask 204 (e.g., polymeric components, and the like) formingnon-volatile compounds. Such non-volatile compounds become re-depositedonto the substrate 200, forming a residue 216 (i.e., post-etch residue).After the etch process, the post-etch residue 216 is typically found onthe etch mask 204, sidewalls 212 of the film stack 202 and elsewhere onthe substrate 200.

[0030] When a metal-containing layer (i.e., layer 208) is etched duringstep 104, the post-etch residue 216 also comprises atoms of such metal(e.g., tantalum (Ta), titanium (Ti), tungsten (W), and the like) and/orcompounds of the metal (i.e., metal chlorides, metal fluorides, metaloxides, metal nitrides, and the like) that may be formed during the etchprocess. In the illustrative embodiment discussed herein, such metalliccompounds may comprise Ta_(x)Cl_(y) (where x and y are integers),Ta_(x)F_(y) (where x and y are integers), and Ta_(x)O_(y) (where x and yare integers), and the like. Metal-containing post-etch residues aregenerally more difficult to remove from the substrate than other typesof residue. Such residues 216 are also considered a contaminant withrespect to subsequent processing of the substrate 200.

[0031] At step 106, the etch mask 204 (e.g., photoresist mask) and thepost-etch residues 216 are removed (or stripped) from the film stack 202and the substrate 200 (FIG. 2C). In one embodiment, the mask 204 andpost-etch residues 216 are removed using a hydrogen-based plasma. Thehydrogen-based plasma may comprise one or more hydrogen-containing gasesincluding hydrogen (H₂), water vapor (H₂O). The hydrogen-based plasma ispreferably a remote plasma (i.e., a plasma that is excited outside thereaction volume of the process chamber), such as a microwave plasmaexcited at about 1.0 to 10 GHz or a radio frequency plasma excited atabout 0.05 to 1000 MHz.

[0032] Step 106 can be performed in a reactor such as an Advanced Stripand Passivation (ASP) reactor of the CENTURA® system. The ASP reactor(described in detail with reference to FIG. 3 below) is a downstreamplasma reactor in which a microwave plasma is confined such that onlyreactive neutrals are provided to the reaction volume of the processchamber. Such plasma confinement minimizes plasma-related damage of thesubstrate or circuits formed on the substrate. Alternatively, step 106can be performed in a DPS reactor or an AXIOM® reactor, both of whichare commercially available from Applied Materials, Inc. of Santa Clara,Calif. The AXIOM® reactor is also a remote plasma reactor and isdescribed in U.S. patent application Ser. No. 10/264,664, filed Oct. 4,2002 (Attorney docket number 6094), which is herein incorporated byreference.

[0033] Using the CENTURA® system, upon completion of step 104, thesubstrate 200 may be transported, under vacuum, from the DPS reactor tothe ASP, AXIOM® or another DPS reactor for performing step 106. As such,the substrate is protected from contaminants that may be present in anon-vacuumed portion of the manufacturing environment.

[0034] In one illustrative embodiment, the etch mask 204 and post-etchresidues 216 are removed in the ASP reactor by providing hydrogen (H₂)at a flow rate of about 1000 to 5000 sccm, water vapor (H₂O) at a flowrate of up to about 50 sccm (i.e., a H₂:H₂O flow ratio ranging fromabout 100% of H₂ to 20:1), applying a microwave power of about 1000 to2000 W at approximately 2.45 GHz and maintaining a wafer temperature atabout 100 to 300 degrees Celsius at a pressure in the process chamber ofbetween about 1 and 4 Torr. The duration of step 106 is generally about40 to 200 sec. One exemplary process provides H₂ at a rate of 3000 sccm,H₂O at a rate of 30 sccm (i.e., a H₂:H₂O flow ratio of about 100:1),applies a microwave power of 1400 W and maintains a wafer temperature of250 degrees Celsius at a chamber pressure of 2 Torr.

[0035] Step 106 strips and volatilizes the etch mask 204 and thepost-etch residue 216. However, after step 106, traces 228 of post-etchresidues 216 and of the etch mask 204 may still remain on the film stack202 and substrate 200. Additionally, in some applications, the plasmastrip process of step 106 may produce a thin film of residue 230 (shownin phantom in FIG. 2C).

[0036] At step 108, the residues 216, 230 are removed from the filmstack 202 and elsewhere on the substrate 200 (FIG. 2D). In oneembodiment, the residues 216, 230 are removed by dipping the substrate200 in an aqueous solution including hydrogen fluoride (HF). In oneillustrative embodiment, the aqueous solution includes between 0.5 and12% by volume of hydrogen fluoride. The hydrogen fluoride solution mayadditionally include between 0.5 and 15% by volume of at least one ofnitric acid (HNO₃) and hydrogen chloride (HCl). After the substrate isdipped in the aqueous solution of hydrogen fluoride, the substrate isconventionally rinsed with deionized water to remove any traces ofhydrogen fluoride. During immersion, the aqueous hydrogen fluoridesolution may be maintained at a temperature of about 10 to 30 degreesCelsius. The duration of the wet dip process is generally between 1 and10 minutes. One specific process uses an aqueous solution that comprisesabout 1% by volume of hydrogen fluoride, at a temperature of about 20degrees Celsius (i.e., room temperature), for a duration of about 5minutes.

[0037] At step 110, the sequence 100 ends.

[0038] The inventive method for removing residues from the substrateuses only one wet treatment step (step 108), and such wet treatment stepis performed after the substrate is removed from a vacuumed portion ofthe manufacturing environment. As a result, in comparable applications,the sequence 100 facilitates about four times higher throughput(measured as a number of wafers processed in a unit of time) thanconventional residue removal techniques.

[0039]FIG. 3 depicts a schematic diagram of the exemplary Advanced Stripand Passivation (ASP) reactor 300 that may be used to practice portionsof the invention. The ASP reactor is available from Applied Materials,Inc. of Santa Clara, Calif. The reactor 300 comprises a process chamber302, a remote plasma source 306, and a controller 308.

[0040] The process chamber 302 generally is a vacuum vessel, whichincludes a first portion 310 and a second portion 312. In oneembodiment, the first portion 310 comprises a substrate pedestal 304, asidewall 316 and a vacuum pump 314. The second portion 312 comprises alid 318 and a gas distribution plate (showerhead) 320, which defines agas mixing volume 322 and a reaction volume 324. The lid 318 andsidewall 316 are generally formed from a metal (e.g., aluminum (Al),stainless steel, and the like) and electrically coupled to a groundreference 360.

[0041] The substrate pedestal 304 supports a substrate (wafer) 326within the reaction volume 324. In one embodiment, the substratepedestal 304 may comprise a source of radiant heat, such as gas-filledlamps 328, as well as an embedded resistive heater 330 and a conduit332. The conduit 332 provides a gas (e.g., helium) from a source 334 tothe backside of the wafer 326 through grooves (not shown) in the wafersupport surface of the pedestal 304. The gas facilitates heat exchangebetween the support pedestal 304 and the wafer 326. The temperature ofthe wafer 326 may be controlled between 20 to 400 degrees Celsius.

[0042] The vacuum pump 314 is adapted to an exhaust port 336 formed inthe bottom 316 of the process chamber 302. The vacuum pump 314 is usedto maintain a desired gas pressure in the process chamber 102, as wellas evacuate post-processing gases and volatile compounds from thechamber. In one embodiment, the vacuum pump 314 comprises a throttlevalve 338 to control a gas pressure in the process chamber 302.

[0043] The process chamber 302 also includes conventional systems forretaining and releasing the wafer 326, end of process detection,internal diagnostics, and the like. Such systems are collectivelydepicted in FIG. 3 as support systems 340.

[0044] The remote plasma source 306 includes a microwave power source346, a gas panel 344, and a remote plasma chamber 342. The microwavepower source 346 comprises a microwave generator 348, a tuning assembly350, and an applicator 352. The microwave generator 348 is generallycapable of producing about 200 W to 3000 W at a frequency of about 0.8to 3.0 GHz. The applicator 352 is coupled to the remote plasma chamber342 to energize a process gas (or gas mixture) provided to the remoteplasma chamber 342 into a microwave plasma 362.

[0045] The gas panel 344 uses a conduit 366 to deliver the process gasto the remote plasma chamber 342. The gas panel 344 (or conduit 366)comprises means (not shown), such as mass flow controllers and shut-offvalves, to control gas pressure and flow rate for each individual gassupplied to the chamber 342. In the microwave plasma 362, the processgas is ionized and dissociated to form reactive species.

[0046] The reactive species are directed into the mixing volume 322through an inlet port 368 in the lid 318. To minimize plasma damage todevices formed on wafer 326, the ionic species of the process gas 364are substantially neutralized within the mixing volume 322 before thegas reaches the reaction volume 324 through a plurality of openings 370in the showerhead 320.

[0047] To facilitate control of the process chamber 300 as describedabove, the controller 308 may be one of any form of general-purposecomputer processor that can be used in an industrial setting forcontrolling various chambers and sub-processors. The memory, orcomputer-readable medium, 356 of the CPU 354 may be one or more ofreadily available memory such as random access memory (RAM), read onlymemory (ROM), floppy disk, hard disk, or any other form of digitalstorage, local or remote. The support circuits 358 are coupled to theCPU 354 for supporting the processor in a conventional manner. Thesecircuits include cache, power supplies, clock circuits, input/outputcircuitry and subsystems, and the like. The inventive method isgenerally stored in the memory 356 as a software routine. The softwareroutine may also be stored and/or executed by a second CPU (not shown)that is remotely located from the hardware being controlled by the CPU354.

[0048]FIG. 4 is a table 400 summarizing the process parameters of theplasma strip process described herein using the ASP reactor. The processparameters summarized in column 402 are for one exemplary embodiment ofthe invention presented above. The process ranges are presented incolumn 404. Exemplary process parameters for the plasma strip processare presented in column 406. It should be understood, however, that theuse of a different plasma reactor may necessitate different processparameter values and ranges.

[0049] The invention may be practiced in other semiconductor systemswherein the processing parameters may be adjusted to achieve acceptablecharacteristics by those skilled in the art by utilizing the teachingsdisclosed herein without departing from the spirit of the invention.

[0050] While the foregoing is directed to the illustrative embodiment ofthe present invention, other and further embodiments of the inventionmay be devised without departing from the basic scope thereof, and thescope thereof is determined by the claims that follow.

What is claimed is:
 1. A method for removing residue from a substrate,comprising: providing a substrate having a metallic residue thereon; andexposing the substrate to a hydrogen-based plasma to volatize themetallic residue.
 2. The method of claim 1 wherein the metallic residuecomprises at least one of a metal-containing residue and a polymericresidue.
 3. The method of claim 2 wherein the metal-containing residuecomprises at least one metal selected from the group consisting oftantalum (Ta), titanium (Ti), tungsten (W) and hafnium (Hf).
 4. Themethod of claim 1 wherein the hydrogen-based plasma comprises at leastone of hydrogen (H₂), water vapor (H₂O).
 5. The method of claim 1wherein the hydrogen-based plasma comprises hydrogen (H₂) and watervapor (H₂O) at a H₂:H₂O flow ratio in a range from 20:1 to 100% of H₂.6. The method of claim 1 wherein the exposing step comprises: providinghydrogen (H₂) and water vapor (H₂O) at a H₂:H₂O flow ratio in a rangefrom 20:1 to 100% of H₂; maintaining the substrate at a temperature ofabout 100 to 300 degrees Celsius at a process chamber pressure betweenabout 1 to 4 Torr; applying about 1000 to 2000 W of microwave power atabout 2.45 GHz to form the hydrogen-based plasma; and exposing thesubstrate to the hydrogen-based plasma for about 40 to 200 seconds. 7.The method of claim 1 further comprising immersing the substrate in anaqueous solution including hydrogen fluoride after exposing thesubstrate to the hydrogen-based plasma.
 8. The method of claim 7 whereinthe aqueous solution comprises between 0.5 and 12% by volume of hydrogenfluoride.
 9. The method of claim 8 wherein the aqueous solution furthercomprises between 0.5 and 15% by volume of nitric acid (HNO₃).
 10. Themethod of claim 8 wherein the aqueous solution further comprises between0.5 and 15% by volume of hydrogen chloride (HCl).
 11. The method ofclaim 7 wherein the substrate is immersed in the aqueous solution forabout 1 to 10 minutes.
 12. The method of claim 7 wherein the immersingstep comprises: immersing the substrate in an aqueous solutioncomprising between 0.5 and 12% by volume of hydrogen fluoride anddeionized water at a temperature of about 10 to 30 degrees Celsius for aduration of about 0.5 to 5 minutes.
 13. A method for removing metallicresidue from a substrate, comprising: providing a substrate having ametallic residue thereon; exposing the substrate to a hydrogen-basedplasma to volatize the metallic residue; and immersing the substrate inan aqueous solution including hydrogen fluoride.
 14. The method of claim13 wherein the metallic residue comprises at least one of ametal-containing residue and a polymeric residue.
 15. The method ofclaim 14 wherein the metal-containing residue comprises at least onemetal selected from the group consisting of tantalum (Ta), titanium(Ti), tungsten (W) and hafnium (Hf).
 16. The method of claim 13 whereinthe hydrogen-based plasma comprises at least one of hydrogen (H₂), watervapor (H₂O).
 17. The method of claim 13 wherein the hydrogen-basedplasma comprises hydrogen (H₂) and water vapor (H₂O) at a H₂:H₂O flowratio in a range from 20:1 to 100% of H₂.
 18. The method of claim 13wherein the aqueous solution comprises between 0.5 and 12% by volume ofhydrogen fluoride.
 19. The method of claim 18 wherein the aqueoussolution further comprises between 0.5 and 15% by volume of nitric acid(HNO₃).
 20. The method of claim 18 wherein the aqueous solution furthercomprises between 0.5 and 15% by volume of hydrogen chloride (HCl). 21.The method of claim 13 wherein the substrate is immersed in the aqueoussolution for about 1 to 10 minutes.
 22. The method of claim 13 whereinthe exposing step comprises: providing hydrogen (H₂) and water vapor(H₂O) at a H₂:H₂O flow ratio in a range from 20:1 to 100% of H₂;maintaining the substrate at a temperature of about 100 to 300 degreesCelsius at a process chamber pressure between about 1 to 4 Torr;applying about 1000 to 2000 W of microwave power at about 2.45 GHz toform the hydrogen-based plasma; and exposing the substrate to thehydrogen-based plasma for about 40 to 200 seconds.
 23. The method ofclaim 13 wherein the immersing step comprises: immersing the substratein an aqueous solution comprising between 0.5 and 12% by volume ofhydrogen fluoride and deionized water at a temperature of about 10 to 30degrees Celsius for a duration of about 0.5 to 5 minutes.